The present invention relates to an ultrasonic imaging apparatus and, more particularly, to an ultrasonic imaging apparatus for performing diagnosis of living organism tissue by utilizing a nonlinear phenomenon and/or a sound velocity caused by an ultrasonic beam passing through a living organism tissue and/or the interaction between an ultrasonic wave and the living organism's tissue.
Various techniques using ultrasonic waves have been proposed for extracting information representing the state of living organism's tissue. A so-called cross-beam method has received a great deal of attention in recent years. This method can measure various acoustic and nonlinear parameters, sound velocity, etc. by crossing an ultrasonic transmission beam and an ultrasonic echo beam.
An ultrasonic diagnosis apparatus using the crossbeam method employs a conventional linear scanning type ultrasonic transducer. The ultrasonic transducer of this type has a transducer array including a large number of ultrasonic transducer elements. This transducer array is divided into first and second transducer groups spaced apart by a predetermined distance. The first and second transducer groups are switched to alternately perform transmission and reception. If the first transducer group serves as a transmission group, drive pulses are supplied to the transducer elements of this transducer group at such different timings as to cause it to emit ultrasonic beams into the living body at a predetermined angle. Waves reflected by the body (i.e., echo waves) are received by the second transducer group. During the transmission and reception operation, a propagation time of the ultrasonic wave from the transmission point to the reception point is measured, and at the same time, voltages of drive pulses are changed to measure a drive voltage dependency parameter of the echo wave received by the second transducer group. The drive voltage dependency parameter varies in accordance with the changes in drive pulse voltage. A nonlinear parameter is calculated from data of drive voltage dependency parameter. The calculated acoustic and nonlinear parameters are used to distinguish normal tissue from abnormal tissue.
In the conventional ultrasonic diagnosis apparatus described above, the data acquired by one cycle of transmission and reception is used as data concerning the state of the tissue in the ultrasonic wave propagation path. For this reason, the abnormal tissue cannot be easily discriminated from the normal tissue by the resultant parameter data.
In actual diagnosis, a wide range of tissue is of interest. In the above ultrasonic diagnosis apparatus, the ultrasonic wave propagation path must be mechanically changed, that is, the ultrasonic transducer must be moved along the body surface. This manipulation is very cumbersome, preventing improvement improvement of diagnostic efficiency.